1. Field of the Invention
The present invention relates to an IP (Internet Protocol) address duplication detection method using an address resolution protocol and, more particularly, to a method of performing duplication diagnosis/detection of IP addresses set in network devices within a single subnet by using an address resolution protocol.
2. Description of the Prior Art
Different IP addresses are respectively assigned to network devices on an IP network. In some cases, however, duplicate IP addresses are assigned to devices.
In general, no address duplication occurs in the assignment of MAC addresses (Media Access Control Addresses=addresses for identifying the respective computers on a LAN) which are hardware addresses basically unique to the respective network devices.
An address resolution protocol (to be abbreviated as ARP hereinafter) is a protocol aimed at acquiring the MAC address of a remote device from an IP address. The present invention uses this ARP as an IP address duplication diagnosis/detection means by exploiting the characteristics of ARP under the condition that there is no MAC address duplication even though there may be IP address duplication.
Note that ARP is a protocol widely used as one of TCP/IP (Transmission Control Protocol/Internet Protocol) protocols, which is an optimal and effective protocol in terms of protocol versatility.
According to an automatic IP address setting method as the first prior art, which is disclosed in Japanese Unexamined Patent Publication No. 11-74915, in a client/server system, after identical IP addresses (default IP addresses) are registered in all clients to be connected, the server sends out an ARP request packet to a client. Upon reception of the packet, the client changes the IP address of its own on the basis of the reception time, and transmits the changed IP address to the server over an ARP reply packet, thereby managing IP addresses on the server.
According to a network device control method as the second prior art, which is disclosed in Japanese Unexamined Patent Publication No. 11-282644, network devices on a network are detected, and the IP addresses of the detected network devices are acquired. One network device is then designated among those on the network. An IP address that should be set for the designated network device is input, and the input IP address is compared with one or a plurality of IP addresses acquired in advance. If an identical IP address is detected upon comparison between the IP addresses, setting of an IP address is stopped. If no identical IP address is detected, the IP address is set, thus preventing IP address duplication with respect to other network devices.
Both the first and second prior arts have the purpose of preventing identical IP addresses from being assigned to a plurality of network devices.
Although different IP addresses are assigned to the respective network devices on an IP network, identical IP addresses may be assigned to devices due to a setting error caused by a network user.
If such IP address duplication occurs in a remote communication apparatus, communication may be performed with an unwanted remote communication apparatus.
Even if communication may be performed with a desired remote communication apparatus by chance, since an ARP cache table for managing the correspondence between remote IP addresses and remote MAC addresses is dynamically updated during communication, the current MAC address may be switched to other unwanted remote communication apparatuses at irregular intervals. In this case, packets cannot reach the desired remote communication apparatus. As a consequence, the established connection is abnormally disconnected.
In consideration of network management, demands have arisen for a method of detecting an IP address duplication fault like the one described above.